Hydraulic pump and motor system



Oct. 25, 1955 J. A. LAUcK 2,721,448

HYDRAULIC PUMP AND MOTOR SYSTEM Original Filed Sept. 7, 1948 3 Sheets-Sheet 1 F' .2 10 NC 61 Af/,V36 \35 35 A// 5@ Zyl/Jos.

@M @Magni/ Oct. 25, 1955 1. A. I AucK HYDRAULc PUMP AND MOTOR SYSTEM Original Filed Sept. 7, 1948 Sheets-Sheet 2 M n f .i ,IF/ w mL Vl QT lm U l. E i f5 Z A n a n a 0 .@W 7\\/ m 3 f-w-N'v Oct. 25, 1955 J. A, LAUCK HYDRAULIC PUMP AND MOTOR SYSTEM Original Filed Sept. '7, 1948 3 Sheets-Sheet 5 [ml .Il H

Va/ve w I fg Fm a W u Y/2/ ,031 a United States Patent() HYDRAULIC PUMP AND MTR SYSTEM John A. Lauck, Shaker Heights, Ohio, assigner to Borg- Warner Corporation, Chicago, Ill., a corporationv of Illinois Original application September 7, 1948, Serial No. 47,992, now Patent No; 2,627,232, dated February 3, 1953. Divided and this application April 4, 1952, Serial No. 280,694

9 Claims. (Cl. Gli- 52) This application is a division of application Serial No. 47,992 for Hydraulic Power Unit, tiled September 7, 1948, now Patent No. 2,627,232, issued February 3, 1953.

This invention relates to power units and more particularly to liquid pressure power units including manually operable control valve means.

Liquid pressure power units including a continuously driven pressure generator, an intermittently operated pres sure responsive motor, and manually adjustable control valve means have been proposed heretofore. However, previously known arrangements have lacked the refinement, sensitiveness, precision of control and efficiency of operation necessary, for example, under the rigid requirements involved in raising and lowering tractor drawn agricultural implements.

ln previously available arrangements, it has been found necessary to either provide a very large ow capacity by-pass valve capable of handling the entire output of the pressure generator almost instantaneously when the delivery of pressure liquid to the motor is to be discontinued; or alternatively, provide means effective to throttle the inlet flow to the generator. The disadvantages and undesirable aspects of each of these previous arrangements have become well known.

It is an object of this invention to provide an improved efficient and effective power unit including means for selectively delivering liquid pressure to a pressure responsive motor; holding said pressure on said motor; and subsequently metering said liquid pressure away from said motor for controlling the return movement thereof.

It is a further object to provide an arrangement of the present character employing an intermeshing gear type pressure generator having pressurable loadable and unloadable end plate and gear journal bearing defining means and manually selective control valve means for maintaining the pressure liquid acting on said end plate means or alternatively relieving t'ne same therefrom depending upon the position of said manual means.

It is a further and more particular object to provide an arrangement of the above character incorporating manually operable control valve means effective in a first position thereof to maintain said loading pressure on said end plate, to thus cause said pressure generator to deliver pressure liquid to said motor; the control valve means being movable a minute distance to a second position effective to instantaneously relieve said loading pressure and cause said generator to discontinue the delivery of pressure liquid to said motor, while locking in place the pressure liquid already delivered to said motor to thus maintain said motor in the position to which the same has been moved; and the control valve means being further movable to a third position effective to meter said delivered liquid away from said motor at a precise rate dependent upon the extent of such movement, while at the same time continuing to relieve the pressure liquid from acting on said end plate bearing and pumping seal defining means.

It is a more specific object to provide an arrangement 2,721,448 Patented Oct. 25, 1955 ICC of the above character wherein said manually selectable control means is in the form of a plunger or spool type valve having a cylindrical housing formed with a plurality of axially spaced ports and including a plunger or spool type valve proper formed with specially arranged axially spaced peripheral valving surfaces for cooperation with said ports.

Other objects, advantages and uses of the present invention will become apparent from the reading of the following specification taken in connection with the appended drawings, which form a part thereof, and, wherein:

Fig. l is a schematic layout view partially in section showing a preferred embodiment of the invention;

Fig. 2 is an enlarged axial cross-sectional view taken substantially on line 2-2 of Fig. 3 showing to advantage the pressure loadable and unloadable generator, and the associated manually selectable control valve arrangement which in combination forms the particular subject matter to which the present invention is directed;

Fig. 3 is a cross-sectional view taken substantially on line 3 3 of Fig. 2;

Fig. 4 is a cross-sectional View taken substantially on line 4--4 of Figs. 2 and 3;

Fig. 5 is a cross-sectional view taken substantially on line 5 5 of Fig. 2;

Fig. 6 is an enlarged broken away View of a portion of Fig. 2 bringing out to particular advantage the novel re lationship and cooperation of the precise form of pressure loaded bushing assembly and the precise form of manually actuatable control valve in combination; and

Fig. 7 is a schematic layout View partially in section showing an alternative somewhat simplified embodiment of the present invention.

Referring in greater detail to the drawings and first to the preferred embodiment of the hydraulic power unit shown in Figs. l through 6, it will be seen that a pump or liquid pressure generator G1 includes a unitary housing 14B enclosing gears 11, 12, and manually actuatable control valve means C1. Generator G1 is adapted to be continuously driven, as for example, by having the usual geared connection 13 with the internal combustion engine of a tractor or other vehicle (not shown) requiring an intermittent supply of pressure liquid for operating a pressure responsive piston motor M1 associated with the vehicle. Liquid from a supply sump S is delivered by generator G1 through conduit 14 to a one-way check valve V1, thence through conduit 16 to motor M1, the latter being adapted to operate a device associated with the vehicle, the present arrangement being particularly suitable for the raising and lowering of a plow or for operating other agricultural implements drawn by a tractor (not shown).

In installations of the present character, it is important that there be provided a very sharp and precise control of the initiation and the discontinuance of pressure liquid delivery by pressure generator G1. To this end the present invention provides in combination, a precise form of pressure generator comprising a liquid pressure loadable and unloadable bushing assembly or end plate means B subject to the novel and improved control valve unit C1, both incorporated in the unitary housing 10.

Manually actuatable control valve unit C1 comprises essentially bore 17 formed in the unitary housing 1f) and having a plurality of axially spaced ports including a port 18 adapted to maintain the left-hand portion of bore y 17 in continuous communication with the sump S through 19 and 21 to provide a plurality of operating conditions as will appear.

Port 19 is in the form of an annular recess in the wall of bore 17 and has a generally rectangular cross-Section, including a forward wall 22 extending substantially at a right angle to the axis of the bore 17. Cooperating with annular port 19 is -cylindrical surface portion 23a of a plunger 23. This cylindrical surface portion 23a terminates in a Aleft kend ,surface 23b likewise extending substantially at a right angle to the axis of bore 17 and forming with the cylindrical surface a very effective valve cooperating with the terminal of valve port wall portion 22 to provide a sharp opening and closing of port 19 requiring only a very minute movement of the plunger. It is very important to the present invention that the opening and closing lof port 19 require only Ya very small axial movement of plunger 23, as will appear from the description of the operation thereof in effecting the loading and unloading of pressure generator G1. As will be apparent hereinafter unloading of the pressure loadable bushing assembly B requires a flow capacity of only a few drops per second through port 19, or only a very small fraction of the fiow rate produced by the gears.

Port 21 is spaced axially to the right of port 19 and may likewise be in the form of an annular recess in cylindrical bore 17. Port 21 is arranged to be closed by cylindrical valving surface 24 of plunger 23 when in opposed relation thereto, and is arranged to be gradually opened for permitting metered return fiow therethrough in accordance with the position of tapered metering surface 26 with respect to the port 21.

Control valve plunger 23 has a plurality `of positions important to the operation of this unit including; a first position in which cylindrical valving surface 23a overlaps port 19 shutting off the relief o-f pressure from pressure loadable bushing or end plate assembly B of pressure generator G1, as will appear, and causes the pressure liquid to hold the bushing B in pumping seal engagement with the adjacent gear side faces with the result that pressure generator G1 is caused to deliver pressure liquid from sump S through check valve V1 to motor M1. Control valve plunger 23 is movable axially a minute distance of the order of 1/@2 to 1/{54 of an inch, to a second position thereof effective instantaneously to permit a suflicient number of drops of liquid to pass away from the rear of bushing B through port 19 past valving surfaces 22, 23a, 23h, and through port 18 to sump S thus permitting bushing B to move in the outward direction to reduce the pumping seal engagement with the gear side face and discontinuing the further delivery of pressure liquid from generator G1 to motor M1. It will thus appear that upon cylindrical valving surface 23a uncovering the terminal of annular groove defining end surface 22, the entire periphery becomes instantly available for the fiow of liquid therepast. This feature, together with the loadable and unloadable bushing feature of generator G1, renders possible the sharp sensitive response with only a very minute axial travel of plunger 23. The fact that annular groove dening surface 22 is substantially parallel to the terminal surface 23b of plunger 12 also adds to the refined operation. In this second position valve plunger 23 continues to be effective through cylindrical surface 24 to maintain port 21 closed and this, together with the one-way action of valve V1, locks the pressure liquid in Contact with the piston of motor M1 and thus holds the same in the position to which it has been previously moved. This locked condition continues to prevail throughout a limited further axial movement of valve plunger 23 which may be referred to as the first zone following the movement of the valve to the second position thereof. Control valve plunger 23 has a third position or range of movement which may more properly be referred to as a second zone of movement. When valve plunger 23 enters the second zone, conical metering valve surface 26 begins to meter the liquid pressure away from motor M1 through conduits 16, 21a, port 21, passages 28, 29 in valve 23, port 18 and .conduit 18a back to sump S, the rate at which this return metering is accomplished being determined by the extent of the axial movement of the valve plunger 23.

The limit of movement of motor M1 in the driven direction thereof may be controlled by the provision of a suitable stop 32 engageable by a complementary stop 33 carried by the piston of motor M1 effective when engaged to move valving surface 23a axially to the right and relieve the loading pressure from acting on bushing B.

The sharply defined opening and closing of port 19 by cylindrical valving surface 23a is very important to the improved operation realized by the present -novel arrangement. The pressure loadable and unloadable bushing B, as will appear, is very sensitive to only a few drops of pressure liquid being relieved therefrom, thus making it practicable to effect the present refined and precise operation by an almost infinitesimal movement of manually actuatable valve plunger 23.

Generator G1 includes pressure loadable and unloadable bushing B and is generally similar vin arrangement and mode of operation to the gear pump construction disclosed and claimed in earlier Roth and Lauck Patent No. 2,420,622 dated May 13, 1947, except for the structure providing for the axial movement of the bushing making practicable the loading and unloading thereof. Essentially, this preferred form of pressure generator includes the intermeshing gears 11, 12 received in bores 36, 37 with radial end walls 3S, 39, 41, 42, said gears having axially oppositely extending journals 11a, 11b, 12a, 12b received in reduced housing bores 36a, 36h, 37a, 37b. Pressure loadable and unloadable bushings B are preferably provided on one side of the gears, the right side being employed in the present installation, while on the other side of the gears there are provided fixed bushings B2. Bushings B are arranged to have a limited axial movement sufficient to permit establishing the desired pumping seal between the inner faces thereof and the gear side faces, and a motive pressure chamber MC is provided to receive pressure generated by gears 11, 12 for holding the bushings in engagement with the gear side faces. Bushings B each preferably comprises an outwardly extending tubular portion 43 received about the corresponding gear journal and within the corresponding reduced housing bore. A fiexible rO-ring seal 44 is interposed between the tubular portion 43 and a stepped recess 44a in the housing bore. Enlarged radial inner flange 46 is coextensive with the gear teeth and has a forward gear side face engaging surface area 47 and a rear pressure actuating surface area 48 defining in part a motive chamber Relief recess 49 is formed in the forward face 47 of the bushing :and is placed in communication with a low pressure area by axial groove 51. The bushings B have a sufficient axial movement to allow a limited slip or by-pass of liquid between the forward face 47 and the gear side face under conditions where the control valve has been operated to discontinue the delivery of liquid pressure .to motor M1, as will appear. While the pressure may be directed to motive chamber MC from the delivery side of the gear teeth in a number of ways, it `is preferred that this be accomplished as disclosed in the above earlier patent by providing an axially extending restricted fiow passage 52 at the position of convergence between the upper and lower bushings B on the outlet side of the gear teeth while closing the corresponding passage by means of a plug 53 on the inlet side of the gear teeth to prevent recirculation.

For the purpose of maintaining gears 11 'and Y12 in engagement with the inner faces of bushings B2 when the Y'loading pressure has been relieved from chamber MC, the journals 11b, 12b are formed with cylindrical recesses 54 receiving coil compression spring 55 and a fioating closure plug 56, the outer terminal of which plug is held in engagement with a fulcrum pin 57 axially supported by the housing of generator G1. Coil compression springs 53 function to urge the bushings in the direction of the gear side faces to thus assure an initial pumping seal engagement prior to the generation of sufficient pressure for acting in motive pressure chamber MC for this purpose.

In practice, the compression values of coil compression springs 58 for effecting the initial pumping seal, and coil compression spring 59 of one-way check valve V1 are specially chosen with reference to one another. Springs 58 are given a compression value such that the pumping seal effect produced thereby will cause the gears to develop :a very low pressure of the order of about 50 to 100 p. s. i. In other words, the bushings, when unloaded, are not completely out of liquid sealing engagement with the gear side faces, this relationship being necessary in order that the generator will respond immediately to :a slight movement of the valve plunger 23 in the direction causing cylindrical surface 23a to overlap and close port 19. Coil compression spring 59 of one-way check valve V1 is therefore given a compression value sufficiently above that of coil compression springs 58 to assure that valve V1 will not open in response to the range of pressure or value of pressure produced by the generator when only springs 58 are acting to urge the bushing into pumping seal engagement with the gear side face. Under this condition, the pressure generator will merely generate a pressure within a range of the order of 50 to 100 p. s. i. and any tendency of the pressure to rise above this value will result in a sufficient movement of the bushing away from the gear side face to prevent any further rise, the liquid then circulating from the outlet side of the gear teeth back to the inlet side thereof, between the gear side face and the associated bushing. Check valve V1 will be opened only when it is desired to transmit liquid pressure to motor M1 as indicated by the operator moving valve plunger 23 to the left and closing port 19 with the result that the liquid pressure builds up within motive Chamber MC, which causes the pressure generated by the gears to supplement the pressure of springs 58 in holding the bushings in pumping seal engagement with the gear side faces. The combined pressures will have a value sufficiently high to cause opening of valve V1 and the delivery of pressure liquid to motor M1.

Turning to Fig. 7, there is disclosed a somewhat simplified embodiment of the present invention as applied to a power unit incorporating both a rotary gear-type pressure generator G2 and a corresponding form of rotary motor M2. Since the liquid pressure for operating motor M2 is supplied continuously and directed therefrom back to the sump S2, when the same is being driven, there is no need for the special provision of means for effecting the return of this pressure liquid from the motor. Therefore, the tapered metering surface, important to the modification of Fig. 1, is not required in this simplified construction.

It will be seen, however, that the broader aspects of the present invention are incorporated inFig. 7 including the pressure loadable and unloadable gear-type generator G2, one-way check valve V2, and the special construction of control valve C2 for selectively causing the loading and unloading of the generator with only a very small or minute travel of plunger 123. Port 119, including radially extending terminal surface 122, corresponds to port 23 and radially extending surface 22 of the modification disclosed in Figs. l through 6. Valving surfaces 123a and 123b of the plunger 123 correspond to surfaces 23a, 2311 of valve plunger 23 of the above modification.

It will be again noted in this alternative form of the invention that due to the unique characteristics of the pressure generator incorporating loadable and unloadable bushings under the control of valve C2 having the specially constructed port 119 and cooperating plunger valving surface 123a, there results a very sharp and refined control of the transition between the on and o delivery condition of the generator G2 with only a very small axial movement of valve plunger 123 of the order of 11%.; to 1/ ,2 of an inch.

What is claimed is:

l. In an arrangement adapted to selectively deliver liquid operating pressure to a pressure responsive motor and return the same therefrom, including a constantly driven liquid pressure generator, means operable to vary the output pressure of said generator, control means comprising a single manually actuatable spool valve received in a cylinder formed with a plurality of axially spaced flow control ports, said spool valve being manually movable to a first position with reference to said ports effective to cause a first operation of said operable means and thereby cause said generator to deliver liquid pressure to said motor, said control valve being movable to a second intermediate position effective to cause a second operation of said operable means and thereby effect the discontinuance of the delivery of liquid pressure from said generator to said motor while at the same time holding the delivered pressure on said motor, said valve being movable to a third position effective to cause return of said liquid pressure from said motor.

2. In a liquid pressure power unit arrangement adapted to selectively deliver liquid operating pressure to a ram type pressure responsive motor and meter return flow therefrom at a selected rate, including a continuously driven intermeshing gear liquid pressure generator, means operable to vary the output pressure of said generator, control means including a manually adjustable spool valve received in a cylindrical bore, a plurality of axially spaced flow control ports in said bore adapted to have the flow therethrough controlled by said spool valve, said spool valve being manually movable to a first position to close a first one of said ports, said operable means being responsive to the closing of said first port and effective to cause said generator to deliver liquid pressure to said motor, said valve being movable to a second position to open said first port and cause said operable means to be effective and said generator to discontinue the'delivery of liquid pressure to said motor while at the same time holding the previously delivered pressure on said motor, said valve having a tapered metering surface for cooperation with a second one of said ports and movable to a third position effective to cause return flow of said liquid pressure from said motor at varying rates depending upon the axial position of said metering surface with reference to said second port.

3. In an arrangement adapted to selectively supply liquid pressure to; hold the pressure on; and return the same from a pressure responsive motor, said arrangement including, a housing containing a pair of intermeshing gears adapted to be continuously driven, a one-way check valve in the outlet from said gears including a first coil compression spring for urging the same in closing direction, axially adjustable end plate means for engaging the gear side faces on at least one side thereof, said end plate means including an outer surface area responsive to the pressure generated by said gears for holding said end plate means in pumping seal engagement, means defining a first restricted flow passage leading from the outlet side of said gears to said outer surface area, a second coil compression spring means effective to urge said end plate means in the direction of pumping seal engagement with a predetermined force sufficient to assure an initial pumping seal engagement and the generation of a first predetermined lcw value of pressure, said value of pressure being below that required to open said one-way check valve against said first spring in the absence of pressure liquid acting on said outer surface area; and means including a second passage which when open is effective to place said rear surface in communication with a zone of relatively low pressure for causing said end plate to be held in pumping seal engagement only by said second coil compression spring means to thus limit said generated pressure to said first predetermined low value; a single manually .operable control valve in said second passage having a flow capacity only a small fraction of the liquid flow produced by said gears, said valve being movable to a first position effective to close communication through said second passage to thus cause said loading pressure liquid to build up and act on said surface area to supplement said second coil compression spring means and hold said end plate means in pumping seal engagement with said gears and cause said gears to generate pressure having a second value above said first value of pressure effective to open said one-way check valve and deliver liquid pressure therethrough to said motor, said manually actuated valve lbeing movable to a second position effective to open said passage and relieve said loading pressure to said zone of relatively low pressure, said valve in said second position being further effective to hold the delivered pressure on said motor, said manually operable valve being movable to a third position remote from said first position effective to cause the return of liquid from said pressure responsive motor, said manually controllable valve being further effective in said third position .to continue maintaining said second passage in open communication during said return fiow.

4. In an arrangement adapted to generate liquid pressure and deliver the same to and return the same from a pressure responsive motor including a housing containing continuously driven intermeshing gears, a one-Way check valve in theoutlet from said gears, axially adjustable end plate means in said housing responsive to the pressure generated by said gears for holding the same in pumping seal engagement, said end plate being axially movable in response to the relief of the loading pressure to -reduce said pumping seal and generating action of said gears; and means including a passage when open effective to place said loading pressure in communication with a zone of relatively low pressure .for causing said end plate to move out `of pumping seal engagement, a single manually operable control valve movable to a first position effective to close communication through said passage to thus cause saidtloading pressure to build up and actuate said end plate into pumping seal engagement with said gear and said pump to deliver pressure liquid to said motor, said manually actuated valve being movable to a second position effective to open said passage and relieve said loading pressure fromacting on said end plate and thus cause discontinuance of pressure generating action, said valve in said second position being further effective to hold the delivered pressure on said pressure responsive device, said manually operable valve being movable to a third position remote from said first position effective to cause the return of liquid from said pressure responsive motor, said manually controllable -valve being further effective in said third position to continue maintaining said passage in open communication during said return flow to thus maintain the discontinuance of pumping action, said manually operable valve comprising a single cylindrical spool, said housing having a cylindrical bore receiving said spool for reciprocable movement therein, a first port cooperating with the inner terminal of said spool for controlling said loading pressure, a second axially spaced port for controlling said return flow, said spool being formed intermediate the ends thereof .with a tapered metering portion adapted to lcooperate With said second port for regulating the rate of return iow from said motor, a third port spaced axially beyond the terminal of said spool adapted to return the Vow lfrom said valve and means defininga passage insaid spool placing said xtapered metering ,portion of said spool in communication with said third port at all times.

Y5. YIn an arrangement adapted to selectively deliver liquid operating pressure to a pressure responsive motor and return the same therefrom, including a constantly driven liquid pressure generator, said generator having a predetermined maximum pressure output and a predetermined minimum pressure output during operation, means operable to vary the output pressure of said. generator, control means comprising a single manually actuatable spool valve received in a cylinder formed with a plurality of axially spaced ow control ports, said spool valve being manually movable to a first position with reference to said ports and effective to cause a Vfirst operation of said operable means and thereby cause said generator to deliver liquid pressure to said motor, said control valve being movable to a second intermediate position effective to cause a second operation of said operable means and thereby lower the output pressure of said generator to cause discontinuance of liquid pressure from said generator to said motor while at the same time .holding the delivered pressure on said motor, said valve being movable to a third position effective yto cause return of liquid pressure from said motor.

6. In an arrangement adapted to selectively deliver liquid operating pressure to a pressure responsive motor and return the same therefrom, including a constantly driven liquid pressure generator having means defining a sealing means effective to vary the output pressure of said generator from a predetermined maximum value to a predetermined minimum value, control means comprising 30 a single manually actuatable spool valve received in a cylinder formed with a plurality of axially spaced oW control ports, the spool valve being manually movable to a first position withreference to said ports effective `to seal said sealing means of said generator to cause .said generator to deliver liquid pressure to said motor at said predetermined maximum value, said control valve being movable to a second intermediate position effective to unseal aforesaid sealing means to lower the output pressure of said generator to aforesaid predetermined minimum to cause the discontinuance of liquid pressure from said generator to said motor, said control valve While in said'second intermediate vposition at the same time holding the delivered pressure on said motor, said valve being'movable to a third position effective to cause the return of D said liquid pressure from said motor.

7. The arrangement as claimed in claim 6 including means defining a tapered metering surface on said spool `Valve effective to vary the rate of liquid pressure returning from said motor depending on the axial position of said metering surface.

8. In an arrangement adapted to selectively deliver liquid under pressure to a pressure responsive motor and return the same therefrom including a liquid pressure generator comprising a pair of intermeshed gears, sealing means adapted to engage said pair vof gears effective to vary the output pressure of said generator from a high to a low value and vice versa, control means comprising a manually actuatable spool valve received in a cylinder formed with a plurality of axially spaced oW control ports, a pressure responsive motor, fluid transmitting means including pressure responsive means interconnecting said generator and said motor, fiuid transmitting means interconnecting said sealing means and at least one of said ports, fluid transmitting means interconnecting said motor and another of said ports; said valve, ports, sealing means and means interconnecting said sealing means and one of said ports being constructed and arranged so that when said valve is in a rst position said sealing means tightly engage said pair of gears and said generator delivers-a high output pressure to' said ymotor through said pressure responsive means; said valve, ports, .sealing means, means interconnecting Vs aid sealing means Vand one of said ports, motor, means interconnecting said motor and the other of `said ports, andsaid pressure responsive means being constructed and arranged so that when said control valve occupies a second position said sealing means are unsealed and said generator delivers a low output pressure and discontinues the application of pressure to said motor through said pressure responsive means while said valve holds the delivered pressure on said motor; said valve, said other of said ports, said motor, and said means interconnecting said motor and the other of said ports being constructed and arranged so that pressure applied to said motor is dissipated when said valve occupies a thirdy position.

9. In an arrangement adapted to selectively deliver liquid under pressure to a pressure responsive motor and return the same therefrom including a liquid pressure generator comprising a pair of intermeshed gears, sealing means adapted to engage said pair of gears eiective to vary the output pressure of said generator from a high to a low value and vice versa, control means comprising a manually actuatable spool valve received in a cylinder formed with a plurality of axially spaced ow control ports, a pressure responsive motor, fluid transmitting means including pressure responsive means interconnecting said generator and said motor, uid transmitting means interconnecting said sealing means and at least one of said ports; said valve, ports, sealing means and means interconnecting said sealing means and one of said ports being constructed and arranged so that when said valve is in a first position said sealing means tightly engage said pair of gears and said generator delivers a high output pressure to said motor through said pressure responsive means; said valve, ports, sealing means, means interconnecting said sealing means and one of said ports, motor, and said pressure responsive means being constructed and arranged so that when said control valve occupies a second position said sealing means are unsealed and said generator delivers a low output pressure and discontinues the application of pressure to said motor through said pressure responsive means.

References Cited in the file of this patent UNITED STATES PATENTS 2,215,115 Buington Sept. 17, 1940 2,229,561 Galanot Jan. 21, 1941 2,293,906 Kvavle et al. Aug. 25, 1942 2,339,001 Clay et al Jan. 11, 1944 2,521,270 Vanni Sept. 5, 1950 2,612,113 Albright Sept. 30, 1952 2,627,232 Lauck Feb. 3, 1953 

